[en] In 1997, United Kingdom Nirex planned to begin construction of an underground Rock Characterisation Facility (RCF) at Sellafield as part of it's ongoing assessment of the suitability of the site as a host for a deep radioactive waste repository. The RCF was to have addressed issues relating to the geology, hydrogeology and geomechanical behaviour of the site by collecting data for testing predictive models and acquiring information only available from an underground situation. In March 1997, the UK Government refused permission for Nirex to begin construction and work at Sellafield was wound down. However, the science design for Phase 1a of the RCF, two vertical access shafts, was completed to provide a set of conceptual designs which address the issues identified by Nirex. By using Sellafield as an example, the designs contribute to a series of reports which demonstrate an approach to validation using an underground facility. This paper describes the Science Design for data collection during shaft construction, which began with the information requirements specified by Nirex on the basis of it's conceptual models and predictive work. It describes the scientific measurements designed to acquire this information and the process of combining the individual measurements into test plans for each shaft. Measurements were planned in the shafts themselves and in boreholes drilled from the shafts. They were designed to provide data on formation porosity and permeability, the geochemistry of formation water and the nature of the fresh-water salt-water interface, shaft inflow, the influence of geological structures on performance, and geomechanical responses to shaft excavation. A key element of the design process was the development of test plans, requiring the co-ordination and integration of the construction and science activities so that both could be carried out in a timely and cost-effective manner